Apex domains cannot have CNAME records.
Question and response
Question
dig trinity.tuxdns.com. NS
Answer
trinity.tuxdns.com. 3 NS ns1.100h.pt.
trinity.tuxdns.com. 3 NS ns2.100h.pt.
Authority
The response has no authority records.
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0